$ B = \left[\begin{array}{rrr}1 & 1 & 0 \\ 0 & 1 & 0 \\ 0 & 2 & 2\end{array}\right]$ What is $ B^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}1 & -1 & 0 \\ 0 & 1 & 0 \\ 0 & -1 & \frac{1}{2}\end{array}\right]$